Predictors of blood ionized calcium concentration in sick adult cattle

Background: Data on the factors affecting blood ionized calcium concentration (ciCa²⁺) and diagnostic performance of serum total calcium concentration (ctCa) measurements to detect abnormal blood iCa²⁺ status are lacking in sick adult cattle. Objective: Assess the association of ciCa²⁺ with venous blood pH, plasma concentrations of chloride (cCl), sodium (cNa), and potassium (cK), and ctCa, and total protein, albumin, and globulin concentrations in sick adult cattle. Animals: Two-hundred and sixty-five adult cattle (≥1-year-old) with different diseases. Methods: Prospective study. Whole blood pH, ciCa²⁺, cNa, cK, and cCl were measured using a blood gas and electrolyte analyzer, whereas ctCa, and total protein, and albumin concentrations were determined using an autoanalyzer. The relationship between ciCa²⁺ and venous blood pH, plasma cCl, cNa, cK, and ctCa, and total protein, albumin, and globulin concentrations was investigated. Sensitivity and specificity were calculated for ctCa for diagnosis of abnormal ciCa²⁺. Results: Sensitivity of ctCa measurements to detect abnormal ciCa²⁺ was 66.0% whereas specificity of ctCa measurements was 72.3%. Serum total calcium concentration measurements accounted for 42% of adjusted blood ionized calcium (iCa²⁺_7.40) concentration variance. Plasma cCl, and cK had explanatory power of ciCa²⁺_7.40, accounting for an additional 21% and 9% of the variance, respectively. Conclusions and Clinical Importance: Serum tCa measurements failed to accurately predict blood iCa²⁺ status in ill adult cattle. Serum tCa concentrations and plasma cCl were the strongest predictors of ciCa²⁺ in sick adult cattle.